A friend has a Range Rover Discovery and fitted new electrics to his trailer. When he connected up all the electrics on the Discovery were blown and he had to take it to the original supplier to have them reset. Cost £150! He has two connectors on the Discovery, one grey and one black. He is now wondering which is the correct one to use? and is there any method of checking if the connection is correct without actually connecting? Blair
black is lighting, grey auxilliaries. the plugs are not identical, so should only go in the right hole.
mrcheerful
isn't (or wasn't) there confusion over whether pin7 was fog/reverse/auxpower on the original black connector, when the grey one was introduced?
What is the purpose of having both black and grey connectors fitted ? Blair
So what's your point ? Are you claiming that Discos are somehow fragile? (funny how the rest of the world manages OK) Or is it really that someone who doesn't even know which connector to use has "fitted new electrics" in such a manner that it broke the tow vehicle and he didn't feel up to fixing it ?
It's just towbar electrics - take it to the shop. He'd already have saved £150 quid by doing this.
There are something like six different European trailer wiring standards 8-(
In the beginning (when Mr Toad got his first caravan) there was a single 12N socket for the lights. This is still around today, as the black socket. If you have a simple trailer, that's all you need. Easy.
Early '70s, and rear fog lamps are invented. These got added to the spare pin on the socket. Life was still (largely) simple.
Then some bright spark decided that car fog laps needed to turn off if there was a trailer right behind them, because of reflections. So the
12N socket sprouted a cut-off switch. Harder to install and unreliable (all towing sockets are unreliable, because they hang out in the road crud - fill them with silicone grease), but the trailer wiring is the same.Then caravans sprouted intenal electrics; batteries that needed charging, fridges and reversing lights (as if any caravan pilot ever learned to reverse a trailer!). Enter the 12S socket with a grey or white cover and a reversed centre pin to stop muppets mis-plugging them into the other socket. Most people used maybe 2 pins and ignored the rest as spares.
Nothing on the 12S is a legal requirement to have when driving (even the reverse) . You can always unplug the 12S and still legally pull the trailer - all AFAIK, but I've had serious grillings from police bottom-inspectors over this and still not been pulled.
Then things got awkward. In 1999 there was a change in the standard to provide a separate earth pin just for the fridge. Fridges use a lot of current, so this was a sensible use for an existing spare pin.
However a c*ck-up was sneaked in at the same time. Before 1999, pin 2 used to be the caravan battery charge feed, controlled by a relay from the ignition, so that it was only live with the engine running. Pin 4 was a permanently live (direct from battery) feed to run interior lights.
After 1999, pin 2 in the caravan plug was redesignated as a short to earth to signal that the plug was connected (!). Yes, change an existing circuit and short circuit the charge relay to earth! What Whitehall moron thought _that_ one up!? The charge relay _should_ be fused, but most tales of caravan wiring explosions have some connection to this changeover. Plug a newer caravan into an old-style car and watch the fireworks.
More annoyingly, there was already a spare pin on 5 which could have been used instead.
Caravan battery charging is now supposed to be done from 4, which isn't ignition controlled. Controlling it (essential) is supposed to be done by a relay in the caravan - which doesn't have any way to tell when the ignition is on. There are lash-ups to get round this - feeding a relay from the sidelights circuit (!) or else "doing it right" and using the fridge circuit to control the relay. However fridge circuits _must_ be wired to support a high current, which is an expensive thing to add to the tow car -- All just to control battery charging.
Some pinout refs
The 13 pin
You can get adaptors for 13 pin to 7, but they have problems
If you have a vehicle like a Disco, get a trailer board with your numberplate already on it and a long cable to a single 12N plug. This, and a bag of tie wraps / baler twine, will let you tow anything. This also works as a cabling tester - the long cable even lets you test brakelights single handed.
Just ignore the 12S connector. Only use the 12S connector for caravans or regularly used trailers, and check its connections together with the right tow vehicle on a per-hookup basis.
On Wed, 8 Dec 2004 13:49:19 -0000, "Blair Malcolm" strung together this:
Wouldn't blow the whole loom though if two of those three were mixed.
Read the post. Black is lighting and grey is auxilliary power, e.g. fridge, caravan interior lighting etc...
I am extremely grateful to you for your very full reply and I feel rather ashamed to have to now admit that my friend misled me. He blew the system by connecting his old trailer which had not been used for some time and he now admits that the connector looked pretty mangy. Having bought a new set of electrics he was nervous of connecting it. Hence the query. I did copy your message to another friend who I know has had trouble in the past with trailer electrics and he is grateful for the information. Regards Blair
Still seems odd - the failure mode of crusty trailer electrics is to stop working, not to "blow up" the car side. To cause damage you'd usually have to mis-wire something.
Another common failure is for the car rear fogs to fail, caused by a duff switch on the trailer socket. Unless you know that the fog lamps are wired through the socket, you'll rarely spot this - it's not usually in the car's wiring diagram.
I never have any trouble with trailer electrics. I keep the plugs and sockets stuffed full of silicone grease. When I store a trailer for the winter , I stick the plug in a tin can with a dessicator bag, wrap it in a couple of metallised plastic bags (tortilla chips) and tape the end.
How new is the disco? A lot of newer vehicles need "enabling" with a testbook computer before extras work, one of our friends had to pay a LOT for having towing electrics fitted by the stealer (not a l-r), he asked if he could fit them himself and was told yes, but well charge you the same price to enable them!
Superb post Andy. I've just been looking at trailer wiring for the tow bar to be fitted to my new to me motor (also a Disco). I got very confused with out of date websites and lots of misleading wibble. I'd already sussed the fridge/charging stuff but the fog lights was a new one.
I've opted for 12N and 12S on the basis that it's easier and cheaper to get it all put in now by the dealer and under warranty rather than faff about adding 12S at some future date should we ever decide that a a caravan is a good idea.
Is that up the mating parts or in the back of the connectors as well? I don't envisage doing much towing but the last thing I want is for the electrics not to work when asked to do so after a year or more... Where do you get decent quantites of silicone grease?
Mainly the little screw terminals for the cable to the socket. I also grease the pin surfaces, but I know it won't stay there and it doesn't really need it.
In my toolbox. Every time I open it the damned tube appears to have started leaking again - so that's time to grease every piece of vehicle electrics again and then throw the tube away - if there's one thing I refuse to have in the workshop it's a _leaking_ tube of silicone. I won't even let the stuff into the woodworking workshop - it ruins finishes.
For a new tube I go to RS.
Having just returned from getting the tow bar fitted I thought I'd look into getting a tube of this 'ere grease to whack into the socket...
Wandered of to the RS site and found 566-730 RS "own brand" contact grease, looking under tech info there is an RS Data Sheet entitled "Electrical Contact Lubrication" (104k pdf, 4 pages). Very interesting reading, seems that silicone grease is not a Good Thing(tm) to use for contact protection/lubrication. Any arcing or other high temperature (eg. friction from movement) produces hard crystals of Silicone Carbide, a very effective abrasive... OK for occasionally used towing connectors this probably isn't an issue but worth bearing in mind for other, more delicate connectors.
Not sure of the half a dozen or so actual silicone greases listed by RS you actually use but probably 494-124 but the first sentance of its description refers to "high insulating" properties... Think I'll be getting pucka contact grease 566-730 at =A32.37 + VAT for a 20ml syringe. B-)
? socket...
I think there are many types of silicone lubricants. The one in my car's diffs certainly suffers very high temperatures. It smells like nothing on earth but I trust it doesn't turn to Silicon (no e) Carbide.
Undoubtedly, the Data Sheet refers to silicone polishes as a possible source of contamination, not just silicone greases that are sometimes applied to contacts for its waterproofing/repellant properties.
Begger, that stray e. I'm well aware of the difference. B-(
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